Getting Candy is easy. All you have to do is buy it from Tom Nook...however, if you want it free, there's a way to get the whole Spooky Series very quickly. It requires a good sense of fashion...

First, you need to get a working "look" (see section below), then you need to go to a villager and speak to them. They will give you Free Candy. While it's easier to buy from Tom Nook, if you already have the outfit, use this method.